1. Field of the Invention
The present invention relates to an image-reading processing apparatus, an image reading apparatus, and an image-reading processing method.
2. Description of the Related Art
A conventional method determines a document region based on a density difference between a ground color of a backing portion of an image reading apparatus and a ground color of a document to perform deskewing, cropping of the document region, determination of an image size, and the like, of image data read by the image reading apparatus.
For example, an image reading apparatus according to JP-A-2001-358914 detects a position and a width of a document from an output from a line sensor to correct a skew of image data read by the line sensor and determines the skew based on a detection result.
An image reading apparatus according to JP-A-8-317138 is an apparatus that arranges a uniform-density material at an image readable position to detect a document size, optically detects a boundary between the material and the document, and detects a document position and a document width.
There is a method that makes the backing portion of the image reading apparatus a white-to-black switching mechanism to automatically recognize a document region and makes a backing portion black in image reading to generate contrast between the backing portion and the document.
An image reading apparatus according to JP-A-2006-229858 reads the front and rear surfaces of the document to recognize binder holes of the document, converts a resolution of a read image to a lower resolution, and detects portions having common characteristic amounts on front-surface and rear-surface images each having the low resolution as holes of the document.
An image reading apparatus according to JP-A-2006-5834 is an apparatus that arranges a plurality of uniform density reference plates at readable positions of a photoelectric conversion unit to detect a document size, reads both the surfaces of the document together with the uniform density reference plates, and detects the document size of one read data depending on a density difference.
However, in the conventional image reading apparatus, when a difference between a density of the backing portion and a density of the document is little, a document region cannot be detected, deskewing, cropping of the document region, determination of the document size, and the like are unsuccessful. For example, in the image reading apparatus according to JP-A-2001-358914 or JP-A-8-317138, when the backing portion is black, and when the ground color of the document has a high density (black or the like), the document region cannot be recognized, and deskewing or cropping is unsuccessful. FIG. 1 is a pattern diagram showing a problem in an identifying process for a document region in the conventional technology.
As shown in the upper-side part (front surface of FIG. 1), the conventional image reading apparatus recognizes a density difference (contrast difference) between the ground color of the backing region and the ground color of the document region of read image to determine the document region. As shown in the upper-side part of FIG. 1, in general, the ground color of the document is assumed to be white, and the backing region has a dense ground color. In this case, a high contrast can be obtained at a document edge portion.
However, as shown in a lower-side part (rear surface) of FIG. 1, when the ground color of the document is a deep color, a sufficient contrast difference between the document and the backing region cannot be obtained, and the document region cannot be identified (the contents of the document is erroneously recognized as a document edge in the lower-side part of FIG. 1). Therefore, deskewing or cropping of the document region is unsuccessful.
In the image reading apparatus according to JP-A-2006-229858, it is assumed that the document is white. When the ground color of the document is blackish, a hole region is unsuccessfully detected. Furthermore, detection accuracy may be deteriorated due to a low resolution, and there is no unit that sets an appropriate resolution depending on an object to be detected.
In the image reading apparatus according to JP-A-2006-5834, to use for switching the uniform density reference plates, a photoelectric conversion unit must be movable in a sub-reading direction. To install the photoelectric conversion unit in an Auto Document feeder (ADF) type image reading apparatus, an increase in cost or size, complication of control, and the like are disadvantageously caused. Even when the image reading apparatus according to JP-A-2006-5834 is used, a ground color of a front surface may have a density (for example, white to white) equal to that of the backing portion for the front surface, and the ground color of the rear surface may have a density (for example, black to black) equal to that of the backing portion for the rear surface. For this reason, the document region cannot be recognized, so that an erroneous detection may be disadvantageously performed.